Production of high concentrated fixing and hardening sirups



Patented Feb. 16, 1943 PRODUCTION OF HIGH CONCENTRATED FIXING ANDHARDENING SIRUPS Garnet Philip Ham, Old Greenwich, Com, assignor toAmerican Cyanamid Company, New York, N. Y., a corporation of Maine NoDrawing. Application November 30, 1940,

Serial No. 367,955

6 Claims.

This invention relates to the production of stock fixers and hardenersfor silver halide photographic material.

In the past photographic fixing and hardening baths containing an alumas well as the soluble sodium thiosulfate and sulfite, were eitherprepared by dissolving the chemicals to form .a

. bath of normal concentration, usually about 250 grams of sodiumthiosulfate to the liter, or the bath is made up in liquid form in whichform it keeps for a reasonably long time. There has been a considerabledemand for high strength sirups that could be diluted with waterespecially by users such as physicians and dentists who are not trainedphotographers and who wish to be able to fix their X-ray films with aminimum of time. Such high concentration sirups are of course of greatadvantage because it is possible to rapidly dilute them with water tothe desired strength without dissolving any chemicals or without havingto store relatively large volumes of normal strength fixing baths.

If it is attempted to prepare high concentration sirups using eithersodium thiosuifate or preferably mixtures containing guanidinethiosulfate which show higher solubility, these sirups cannot be readilymade by dissolving up the various ingredients in the normal manner. Onthe contrary, when it is attempted to make such sirups containing forexample 1000-1200 grams of thiosulfate to the liter, precipitation takesplace.

According to the present invention I have found that if the thiosulfateand part of the sullite are dissolved separately and the alum, acid,

and remainder of the sulflte dissolved in a separate solution, and thenmixed, prefer-ably cold, no precipitation results and stable highconcentration fixing sirups are obtained.

It is not desired to limit the present invention to any theory of actionbut it is my opinion that probably a factor of importance lies in theavoidance of excessive local concentrations where some of the solidmaterials are dissolving. The two solutions mix rapidly and completelyand excessive concentrations in isolated zones are not obtained. It isof course possible that other factors may be present and may even be ofgreater importance.

Excellent sirups can be prepared as described above, but when guanidinethiosulfate mixtures are prepared by using the portions of guanidinenitrate with sodium thiosulfate, the sirups are sometimes not completelyclear although usable. If, however, they are filtered throughunactivated wood charcoal; they are completely clear and show excellentstability. I do not wish to lim this feature of the invention to. anyparticular theory but I am of the opinion that an important factor liesin small amounts of impurities which are usually associated withtechnical guanidine nitrate and which are probably adsorbed or removedby the charcoal filtration. When perfectly chemically pure guanidinenitrate is employed, the filtration is not normally required. Thisfeature, while not an essential to the invention is of large practicalimportance as it permits the use of technical guanidine nitrate with acorresponding very marked saving in cost and therefore forms part of thepreferred embodiment of the present invention.

By means of the present invention it is possible to obtainfixing sirupscontaining guanidine thiosulfate up to about 1000-1200 grams ofthiosulfate per liter. Higher concentrations may be produced by theincorporation of hydrotropic materials such as urea. In the present caseI do not claim the addition of hydrotropes generally as this forms thesubject matter of the copending patent of Ham and Barnes No. 2,248,905,issued July 8, 1941.

The invention will be described in. conjunction with the followingspecific examples.

EXAMPLE 1 Two solutions were prepared as follows:

Solution A Parts Water 700 Sodium sulfite (anhydrous) 30 Sodiumthiosulfate (5H2O) 1000 Guanidine nitrate 208 Solution B Parts Water 300Acetic acid (28%) 200 Boric acid 30 Potassium aluminum sulfate 60 Sodiumsulfite 32 portrait film in approximately 2 minutes and X-ray film inabout 1 /4 minutes. The sirup shows excellent stability and at roomtemperature does not show any precipitation after 30 days. At highertemperatures, however, about 49 C., considerable suliurization resultsafter about six days.

When the same materials are used but the solids dissolved in theorder-sodium sulfite, guanidine nitrate, sodium thiosuliate, aceticacid, boric acid, potassium aluminum sulfatea heavy precipitation wasformed containing precipitate showing sulfur and an-aluminum complex.Even after filtering a precipitate reappears.

Higher stability especially at high tempera tures may be obtained byincorporating 36 parts of urea in solution A before filtering throughcharcoal. This sirup is not only completely stable at room temperaturebut also at 6 C. and 49 C. respectively. Difliculty is encountered evenwith the powerful hydrotropic substance, urea, if the ingredients aredissolved one after the other without preparing the two separatesolutions. Other hydrotropes such as those described in the Ham andBarnes patent above referred to, may be substituted for the urea.

A concentrated fixer and hardener sirup was prepared by forming thefollowing two solutions:

Solution A Parts Water 350 Sodium thiosulfate (H:O) 600 Sodium sulfite(anhydrous) 15 Solution B Parts Water 150 Acetic acid (28%) 100 Boricacid 15 Potassium aluminum sulfate 30 Sodium sulflte (anhydrous) 16 Thesolutions were mixed together,

through unactivated charcoal as described in the preceding example, andgave a satisfactory fixing and hardening solution when diluted withwater. In the above examples potassium alum is used and in a similarmanner chrome alum may be employed although the stability of the resulting solution is not quite as high. a

What I claim is:

1. A method of preparing a high concentration stable fixing andhardening solution for silver halide photographic material containing asoluble thiosuliate in amounts of the order of magnitude of 1000 to 1200grams per liter. sulfite, and alum hardener which comprises dissolvingin water the desired amount of soluble thiosul fate and at least aconsiderable portion 01' the sulfite, separately dissolving in water thealum hardening ingredients under acid conditions, and mixing the twosolutions together.

2. A method of preparing a high concentration stable fixing andhardening solution for silver halide photographic material containing asoluble thiosuli'ate in amounts of the order of magnitude of 1000 to1200 grams per liter including guanidine thiosuli'ate in effectiveamounts, sulfite, and alum hardener which comprises dissolving in waterthe desired amount of solublethiosuli'ate and at least a considerableportion 01' the sultite, separately dissolving in water the alumhardening ingredients under acid condi tions, and mixing the twosolutions together.

3. A method according to claim 1in which a hydrotropic substance isincorporated in the first solution.

4. A method according to claim 2 in which a hydrotropic substance isincorporated in the first solution.

5. A method according to claim 1 in which urea is incorporated inamounts sufiicient to exert a hydrotropic action onvthe thiosuliate.

6. A method according to claim 2 in which urea is incorporated inamounts sufiicient to exert a hydrotropic action on the thiosuii'ate.

GARNET PHHJP HAM.

